1. Field of the Invention
The present invention relates to a light guiding apparatus, and a backlight assembly and a liquid crystal display having the same, and more particularly, to a backlight assembly and a liquid crystal display having a light guiding apparatus capable of reducing thickness of the backlight assembly and the liquid crystal display.
2. Description of the Related Art
Generally, information processing equipments require a display device to visually display the processed information to users. Liquid crystal display devices have been developed to have full-color and high-resolution functions with lightweight and compact size compared with CRT-type display devices. As a result, the liquid crystal display devices have been widely used as a monitor of a computer, a household wall-mountable television and various information processing devices.
FIG. 1 is a sectional view showing a structure of a liquid crystal display device, and FIG. 2 is a sectional view showing a structure of a diffusion sheet shown in FIG. 1.
As shown in FIG. 1, a liquid crystal display device 80 includes a display unit 50 for displaying images and a backlight assembly 60 for supplying light to the display unit 50.
The display unit 50 has a liquid crystal display panel 59, data and gate printed circuit boards (not shown), and data and gate tape carrier packages (not shown).
The liquid crystal display panel 59 includes a thin film transistor substrate 52, a color filter substrate 54 and liquid crystal (not shown).
The thin film transistor substrate 52 is a transparent glass substrate on which thin film transistors are arranged in a matrix shape. Data lines and gate lines are connected to the sources and the gates of the thin film transistors, respectively. In addition, pixel electrodes are comprised of ITO (Indium Tin Oxide) of transparent conductive material, and are connected to the drains of the thin film transistors.
The color filter substrate 54 is arranged oppositely to the thin film transistor substrate 52. The color filter substrate 54 has RGB pixels. The RGB pixels show predetermined colors when light passes through the RGB pixels, and are formed through a thin film process. Common electrodes, made of ITO, are coated on a surface of the color filter substrate 54.
When an electric power signal is applied to the gate and the source of the thin film transistor, the thin film transistor is activated, and an electric field is formed between the pixel electrodes of the thin film transistor substrate 52 and the common electrodes of the color filter substrate 54. The electric field changes an aligning angle of the liquid crystal disposed between the thin film transistor substrate 52 and the color filter substrate 54. Thus, a transmissivity of the light passing through the liquid crystal is varied depending on the aligning angle of liquid crystal, so that desired images can be displayed.
The backlight assembly 60 is disposed below the display unit 59, and uniformly supplies lights to the display unit 59. The backlight assembly 60 includes a lamp unit 10 for generating light, a light guiding plate 20, optical sheets 40, and a reflection sheet 30. The light guiding plate 20 changes a path of the light, and guides the light towards the display unit 59. The optical sheets 40 receive the light emitted from the light guiding plate 20, and provide a uniform brightness of light. The reflection sheet 30 is disposed below the light guiding plate 20, and reflects the light leaked from the light guiding plate 20 towards the light guiding plate 20 to improve the efficiency of light.
Although not shown in FIG. 1, the liquid crystal display device 80 further includes a mold frame for sequentially receiving the display unit 59 and the backlight assembly 60, and a top chassis, facing the mold frame and being combined with to the mold frame, for preventing the display unit 59 from being separated from the mold frame.
The optical sheets 40 include a diffusion sheet 42, first and second light-collecting sheets 44 and 46, and a protection sheet 48. The diffusion sheet 42 receives the light emitted from the light guiding plate 20, and provides light having a uniform brightness distribution. The first and second light-collecting sheets 44 and 46 receive the light emitted from the diffusion sheet 42, and collect the light to output the light toward different directions, so that viewing angle is enhanced. The protection sheet 48 is disposed on an upper portion of the second light-collecting sheet 46, and prevents impurities from penetrating into the second light-collecting sheet 46. A scattering agent is added to the diffusion sheet 42 in order that the light emitted from the light guiding plate 20 is diffused to have a uniform brightness distribution.
As shown in FIG. 2, the diffusion sheet 42 has a base layer 42a and a first and second diffusion layers 42b and 42c. The first and second diffusion layers 42b and 42ccover lower and upper layers of the base layer 42a, respectively. A plurality of beads 42d is interposed in the first and second diffusion layers 42b and 42c, so that the diffusion sheet 42 is not closely adhered to the light guiding plate 20.
Since the optical sheets 40 require many sheets (elements), such as the diffusion sheet 42 and the first and second light-collecting sheets 44 and 46, in order to enhance the viewing angle and the brightness characteristic of light, the cost for manufacturing the liquid crystal display device 80 increases, and there is some limits to manufacture the liquid crystal display device 80 having the lighter weight, thinner thickness and compacter size.